The present invention relates to systems for transporting particulate materials, and more particularly to a system for feeding such materials from a hopper with delivery by discharge along with a pressurized gas.
It is commonly known to incorporate a mechanical agitator or stirring device in a hopper for promoting uniform and controlled distribution of a particulate sold such as powder or pellets. It is also known to impart vibratory motion to a hopper or its contents for creating a zone of liquidation or fluidization proximate an outlet of the hopper, thereby avoiding the formation of a "bridge" or "rat hole" that would impede further movement of the material from the hopper. For example, a pneumatic vibrator is disclosed in U.S. Pat. No. 3,363,806 to Blakeslee et al. Also, U.S. Pat. No. 4,383,766 to Eriksson discloses a stream of air that is fed into the lower portion of a hopper through patches of porous material, for fluidizing a powder to be fed from the hopper. U.S. Pat. No. 4,118,074 to Solt discloses the use of pulsating air for vibrating a conveyer that transports a particulate material. It is also disclosed in Bulk Solids Handling by C. R. Woodcock and J. S. Mason that clogging is avoided by periodic blasts of air into a hopper through an auxiliary opening proximate an outlet of the hopper.
A disadvantage of each of these agitators of the prior art is that they contribute significant complexity and expense to the systems with which they are used. The use of such agitators also involves the expenditure of significant energy resources, there being a compromise between the rate of energy consumption and the reliability of the agitation. Also, the use of a mechanical agitator within the hopper assists only locally, yet shaking the whole hopper tends to compact the contents, which undesirably promotes bridging.
In an important class of systems for pressure-discharge of particulates, pellets or particulates of a hygroscopic or deliquescent material are used, often in a very cold or frozen condition. Agitation of this class of particulates is undesirable, because of the resultant wear and pulverization of the particles. The heating associated with the agitation is also undesirable. Also, the incorporation of thermal insulation in the design of the hopper is made more difficult by the presence of agitator components. Further, the introduction of air into the hopper should be minimized for avoiding deleterious heat and/or moisture exchange with the pellets.
Thus there is a need for a particulate delivery system that effectively and reliably feeds the material while avoiding the disadvantages of the prior art.